Turbocharging of Internal Combustion Engines: One of the long-term goals of the automotive manufacturers is to reduce fuel consumption and emissions of modem automotive vehicles powered by internal combustion engines (ICE) while increasing engine efficiency. One approach to reaching this goal is reducing the ICE displacement. However, smaller engines having reduced swept volume typically exhibit insufficient power and torque when operating with normal aspiration. This problem can be remedied by supercharging. It is well known in the art that ICE power output increases with increased weight of air ingested into engine cylinders and available for combustion. Weight of intake air ingested into engine cylinders can be increased by either (1) increasing the pressure of intake air beyond what can be accomplished by natural aspiration or by (2) reducing the temperature of intake air or by (3) a combination of (1) and (2). A supercharged ICE, therefore, receives combustion air with higher density than a normally aspirated ICE. As a result, supercharging allows generating increased power from an engine of a given displacement or, generating a given power output from an engine of smaller size, weight, cost, and emissions. In addition, reduced charge temperature is known to reduce ICE emissions by decreasing charge pre-ignition also known as knocking.
One commonly used type of a supercharger is the exhaust-gas turbocharger which typically includes a turbine and a centrifugal compressor on a common shaft. The turbine is rotated by exhaust gases from the engine and spins the compressor. The compressor receives intake air, compresses it, and supplies it to ICE combustion chamber(s). Turbochargers provide the advantages of relatively smooth transition from natural aspiration to supercharged operation while utilizing some of the residual energy of hot exhaust gas, which would otherwise be largely wasted. The challenges of constructing a turbocharged ICE include: 1) reducing as much as possible the response time lag, 2) broadening of the compressor working regime, and 3) reducing the exposure of compressor impeller to high temperatures and stresses. Information relevant to attempts to overcome these challenges and the disadvantages of such attempts are described below.
A turbocharged ICE is susceptible to a slow response time known as the “turbo lag” which is caused by the low pressure and low quantity of exhaust gases that are available to operate the turbine at low engine speeds. This translates to insufficient quantity of intake air delivered to the engine and results in insufficient torque at low engine speeds. The turbo-lag problem may be corrected in-part by the use of a variable nozzle turbine, which alters the cross-sectional area through which the exhaust gas flows in accordance with engine speed. However, this approach adds complexity and cost while reducing reliability. Another approach to reducing the turbo lag may use one or more jets of air injected onto the compressor wheel of a turbocharger as disclosed, for example, by Williams et al. in U.S. Pat. No. 3,190,068. Such air jets may be directed generally onto the vanes of the compressor wheel so as to transfer a part of their momentum to the wheel and thus accelerate the rotational speed of the compressor. Air injected in this manner becomes a part of the intake air ingested by the engine. Yet another approach may use air jets injected into the diffuser part of the compressor as disclosed by Schegk in U.S. Pat. No. 5,461,860, the entire contents of which is hereby expressly incorporated by reference. Neither said Williams nor said Schegk disclose injection of cold air into compressor housing or compressor components.
Performance of a turbocharger compressor is often described in terms of a characteristic diagram which defines the working range of the compressor by plotting the ratio of compressor output pressure to its input pressure as a function of the air mass throughput through the compressor. The compressor working range in the characteristic diagram is limited by a so-called “surge limit.” The surge limit represents a characteristic curve which curbs the output of the compressor in the regime of combined low mass throughputs and a high output pressure. This regime corresponds to an ICE operating at high load and a low rotational speed. With the compressor operating close to the surge limit, local zones of detached flow may be formed, which may result in periodic pulsation of the flow, change in the flow direction and acoustic noise. To increase the operating range of the compressor in the regime of high-loads and low-speeds it is desirable to shift the surge limit towards lower mass throughputs. The surge limit may be favorably shifted by means of characteristic-diagram stabilization measures such as a bypass which bridges compressor outflow port and inflow port. In particular, the bypass returns part of the compressor output flow into the compressor the inflow port and directs it on the compressor-impeller inlet edge as disclosed, for example, by Sumser et al. in U.S. Pat. No. 6,813,887 the entire contents of which is hereby expressly incorporated by reference. If the compressor operates close to the surge limit, the bypass allows recirculation of a predetermined portion of the compressor output stream back to the compressor inflow port. Sumser also discloses an ICE having an auxiliary air feed which supplies auxiliary air at ambient temperature through an injection opening in a wall of the compressor inlet and directs it into the flow-facing region of the compressor wheel. Auxiliary air injected in this manner influences the surge limit in favor of a regime with lower mass throughputs and high compressor pressure ratio. As a result, compressor working range is broadened. Furthermore, injected auxiliary air beneficially drives the compressor impeller, thereby helping the turbocharger to accelerate to its normal operating speed range. As a result, high charging pressures may be attained more rapidly, the undesirable turbo lag is reduced, and the turbocharged ICE may accelerate from low speed in a rapid, smooth manner. However, said Sumser does not disclose injection of cold air into compressor housing or compressor components.
Experience shows that when turbocharger delivers high supercharging pressures, the compressor components experience high thermal loading. This may necessitate that such components are either fabricated from high-temperature materials, which are costly and difficult to machine or that such components are actively cooled, which has limited effect and adds complexity. This problem may be alleviated by cooling the air recirculated via a bypass from the compressor outflow port back to the compressor inflow port as disclosed by Scheinert in U.S. Pat. No. 7,021,058 the entire contents of which is hereby expressly incorporated by reference. In particular, Scheinert discloses a temperature reducing unit comprising a diffuser in a form of an expansion duct employed to cool the recirculated air before it is directed onto compressor wheel. However, temperature reduction achievable by Scheinert's temperature reducing unit is very limited.
Vortex Tube for Cooling of ICE Intake Flow: Vortex tube is a well known cooling device in the art of refrigeration. Traditional vortex tube comprises a slender tube having one end closed except for a small a central opening and the other end plugged except for an annular opening which may be adjusted in size for flow control, see FIG. 1. A stream of high-pressure air (or other suitable gas) is injected through an inlet port tangentially into the tube in the proximity of the central opening. Resulting vortex flow pattern inside the tube separates the input air stream into a relatively hot air stream which exits through the annular opening and a relatively cold air stream which exits through the central opening and the cold outlet port. Relative flow rates and temperatures of these two streams are typically adjustable by controlling the flow of the hot exhaust stream. See, for example, article entitled “The Vortex Tube as a Classic Thermodynamic Refrigeration Cycle,” by B. K. Ahlbom et al., published in Journal of Applied Physics, Volume 88, Number 6, pp. 3645-3653, Sep. 15, 2000. A variant of the traditional vortex tube suitable for generating only a cold output stream can be produced by entirely closing one of the tube ends combined with active cooling of the tube exterior surface such as shown in FIGS. 2A and 2B and disclosed, for example, by Zerr in U.S. Pat. No. 4,612,646. Suitable cooling may be provided by a cooling jacket which may envelop the exterior surface of the tube. Suitable coolants may be provided in liquid or gaseous form. The exterior surface of the tube can be further provided with surface extensions to facilitate improved heat transfer as disclosed, for example, by Tunkel et al. in U.S. Pat. No. 5,911,740.
Lindberg et al. in U.S. Pat. No. 6,247,460 discloses an ICE having a vortex tube for cooling intake air. Lindbergh's vortex tube generates both cold and hot outputs with only the cold output supplied to ICE intake. All of the intake air flows through the vortex tube at all times. When used on a supercharged ICE, the pressure drop of intake air inside the vortex tube robs the ICE of the pressure boost provided by the supercharger and wastes much of the supercharger output into vortex tube hot flow. Similarly, when used on a naturally aspirated ICE, the vortex tube impedes intake air flow thereby significantly reducing the intake air pressure. In each case the benefit of providing cooler air to the ICE is accomplished at the expense of reducing the intake air pressure. In particular, data of some vortex tube manufacturers suggests that the pressure ratio between vortex tube inlet port and its cold outlet port should be at least 2.4. See, for example, Catalog No. 21, page 102, published by Exair Corporation, Cincinnati, Ohio. Since cooling of the intake air and reducing its pressure have opposite effects on air density, the net benefit of Lindberg's apparatus, if any, is rather limited. Holman et al. in the U.S. Pat. No. 6,895,752 discloses a turbocharged ICE with an exhaust gas recirculation (EGR) system wherein ICE exhaust is directed to a vortex tube to generate a cooler flow and a hoter flow. The cooler flow is directed to ICE intake to recirculate part of the exhaust gas while the hot flow may be exhausted from the ICE in a conventional manner.
In summary, prior art does not teach a turbocharged ICE system that is effective during the conditions of high torque and low engine speed, has a fast response to power demand, is simple, economical, avoids exposing compressor components to excessive temperatures, and reduces susceptibility to charge pre-ignition. Furthermore, the prior art does not teach a turbocharged ICE system where turbocharger operation is augmented by injection of cold air from a vortex tube. Moreover, the prior art does not teach a turbocharged ICE system where turbocharger compressor is cooled by cold air from a vortex tube. It is against this background that the significant improvements and advancements of the present invention have taken place.